Originally posted by Postumus Vented Lens Hoods ~ WHY?
Because lenses need to breath, just like you or I!
Actually, it is to provide a small peek space for the viewfinder when used on non-reflex cameras. The photos below might help since both show the viewfinder window and the "vent" slot.
Without the slots, the edge of the hood intrudes into the viewfinder frame.
P.S. Ventilated hoods are seldom, if ever, used with focal lengths shorter than 35mm on 35mm film (24mm on APS-C) .
Steve
Last edited by stevebrot; 03-14-2020 at 04:19 PM.